Tissues from portions of the male reproductive system of rhesus monkeys will be examined by light and electron microscopy to determine if morphological alterations occur following vasectomy. Tissues to be examined include testis; epididymis; vas deferens; prostate and seminal vesicle. In addition to alterations in morphology, the effect of vasectomy upon the integrity of the blood-testis barrier will be assessed using lanthanum tracer techniques. The animals to be studied have been unilaterally vasectomized by a variety of techniques designed either to maximize or minimize sperm spillage at, or subsequent to the time of surgery, and therefore to maximize or minimize the opportunity for eliciting an immunological response and concomitant morphological alterations. It is hoped that the research may contribute basic information which may be ultimately applicable to the clinical choice of mode of vasectomy having the least immunological and morphological effects in man.